The effect of altering maintenance diet on demand for reinforcers.

Abstract

Six hens’ preferences between whole grain wheat, commercial laying pellets and puffed wheat were assessed using a free-access procedure. Wheat was found to be the preferred food of three hens, pellets were preferred by one, puffed wheat was found to be not preferred by four, and two hens had no preference for any food. The hens were then maintained at 80% ± 10% of their free-feeding body weights by one of the three foods while responding under a progressive ratio schedule in which the response requirement doubled after each reinforcer. A session terminated after a hen had ceased responding for 300 s. All three foods were used as reinforcers and then the maintenance food was changed. Thus all three foods served as reinforcers with each of the three maintenance diets. Response rates, post-reinforcement pauses and demand functions (i.e., the relation between estimated consumption rate and response requirement) under each response requirement were examined. Performance was not affected systematically across hens by diet or reinforcer type. There were no systematic relations between the individual hen’s food preferences and any of the performance measures. The same hens were then maintained at 80% ± 10% of their free-feeding body weight by pellets and responded under fixed ratio schedules with the response requirement doubling each session until a hen received no reinforcers in a session. Sessions terminated after 40 reinforcers or 40 min. Each of the three foods served as the reinforcer for two series of the increasing fixed ratio schedules. The resulting demand functions did not differ over reinforcer type and no relation found between the type of reinforcer and the individual hen’s preferences. Performance (including the shape of the demand functions) was found to be similar under both the progressive and fixed ratio schedules. It is suggested that the provision of post-feed outside of the experimental sessions and the hen’s low body weights could explain why there was no difference in demand between conditions with different maintenance diets and reinforcer types.